The invention relates to photoaddressable side group polymers in which a high birefringence can be induced by irradiation, so that they are suitable for the production of components for storage of optically available information or as optically switchable components.
Photoaddressable side group polymers which have been recommended are special branched polymers: side groups of different types, of which one type (called xe2x80x9cAxe2x80x9d) can absorb electromagnetic radiation and another type (called xe2x80x9cMxe2x80x9d) is a mesogenic group anisotropic in shape, are positioned on a linear backbone, connected via molecular parts which act as spacers.
So that the interaction of the mesogenic groups is not impeded, in the past the mesogenic groups have usually been coupled to the spacing group via an oxygen atom, because it has been assumed to date that higher-valency atoms with their substituents in this position impede the interaction and therefore the photoaddressability because of their steric requirement.
The mechanism of photoaddressed orientation is probably based on the possibility of achieving an orientation of the mesogenic groups and therefore a change in the state of order by electromagnetic radiation. However, the photoaddressable polymers known to date still have the disadvantage that the changes in the state of order which can be produced are too small, the change in the state of order takes place too slowly and/or the patterns written in slowly fade again during storage.
The object of the invention was therefore to provide polymers which do not have these disadvantages or have them to a lesser extent.
Surprisingly, a connection has now been found between the experimentally determinable interaction of the group A, which can absorb electromagnetic radiation, with respect to a standard and the quality of the photoaddressability of the polymer. This finding allows the suitability of the groups A to be tested before their incorporation into the polymer.
The invention thus relates to polymers which have a main chain which acts as a backbone and, branching therefrom, covalently bonded side groups of the formulae
xe2x80x94S1xe2x80x94T1xe2x80x94Q1xe2x80x94Axe2x80x83xe2x80x83(I) and
xe2x80x94S2xe2x80x94T2xe2x80x94Q2xe2x80x94Mxe2x80x83xe2x80x83(II)
wherein
S1 and S2 denote the atoms O or S or the radical NR0,
R0 denotes hydrogen or C1-C4-alkyl,
T1 and T2 denote the radical (CH2)y, which can optionally be interrupted by
xe2x80x94Oxe2x80x94, xe2x80x94NR0xe2x80x94 or xe2x80x94OSiR02Oxe2x80x94 and/or can optionally be substituted by methyl or ethyl,
Q1 and Q2 denote a direct bond, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONR0xe2x80x94, xe2x80x94NR0COxe2x80x94 or xe2x80x94NR0xe2x80x94, or
S1T1Q1 or S2T2Q2 denotes a bivalent group of the formula 
A denotes a unit which can absorb electromagnetic radiation,
M denotes a mesogenic unit anisotropic in shape and
y denotes an integer from 2 to 12,
characterized in that A has an extinction modulus E of greater than 0.2 (measured as described below).
For the purposes of the invention, the value xcex94xcex94E is measured on a compound of the formula Hxe2x80x94Q1xe2x80x94A or HS1T1Q1A wherein Q1, S1, T1 and A have the abovementioned meaning and H represents the hydrogen radical.
The extinction modulus xcex94xcex94E is determined from the changes in extinction xcex94E of the longwave flank of the absorption band of 3 solutions of the following substances, that is to say
Solution A Hxe2x80x94Q1xe2x80x94A or HS1T1Q1A is dissolved in the lowest possible concentration in a solvent which has the lowest possible polarity. The concentration is preferably chosen here such that the steepest possible edge results when the absorption is measured. In the case of dyestuffs, which as a rule have a high molar extinction, this concentration is preferably 10xe2x88x923 molar.
Solution B The standard is dissolved in the same solvent in the highest possible concentration, preferably 1 molar, and the absorption edge is recorded.
Solution C This solution comprises Hxe2x80x94Q1xe2x80x94A or HS1T1Q1A and the standard in the concentrations of solutions A and B.
3 absorption edges are thus obtained: that of the standard, which in general is at a short wavelength, and the absorption edge of solution A and the edge of solution C, which is shifted parallel to this to a long wavelength.
On the longest-wavelength edge, that is to say of solution C, the wavelength belonging to the extinction 0.8 defines the reference wavelength xcex The extinction values E of the three solutions A, B and C are now in each case read off at the wavelengths xcex and xcex+50, where
Esolution C greater than Esolution A greater than Esolution B.
To determine the value of xcex94E, the following differences are obtained for the wavelengths xcex and xcex+50:
xcex94EA=E(xcex)solution Axe2x88x92E(xcex+50)solution A
xcex94EB=E(xcex)solution Bxe2x88x92E(xcex+50)solution B
xcex94EC=E(xcex)solution Cxe2x88x92E(xcex+50)solution C
From these three differences, the increase in extinction of the dyestuff due to the presence of the standard is obtained as the difference xcex94xcex94E:
xcex94xcex94E=xcex94ECxe2x88x92(xcex94EB+xcex94EA)
The standard should be as polar and/or polarizable as possible. The polarity of the solvent should be as low as possible.
In a preferred form, 1,3-dinitrobenzene is used as the standard and dioxane is used as the solvent.
As explained above, A should be able to absorb electromagnetic radiation. The absorption maxima (xcexmax) of preferred groups A can be in the near IR, in the range of visible light or in the UV, preferably in the wavelength range of 320-1500 nm, in particular 350 to 800 nm. Where the terms xe2x80x9cchromophorexe2x80x9d or xe2x80x9cdyestuffxe2x80x9d are used in the context of this invention, they are not limited to the wavelength range of visible light, but are based on the groups A.
Groups A, which give xcex94xcex94E values above 0.2, can be chosen from the radicals of the following classes of dyestuffs (cf. for example, G. Ebner and D. Schulz, Textilfarberei und Farbstoffe [Textile Dyeing and Dyestuffi], Springer-Verlag, Berlin Heidelberg 1989):
I. Azo dyestuffs
1. Monoazo dyestuffs, such as, for example
C.I. Mordant Yellow 1
C.I. Mordant Blue 78
C.I. Disperse Blue 79
C.I. Disperse Yellow 5
2. Disazo dyestufs, such as, for example,
C.I. Mordant Yellow 16
C.I. Disperse Yellow 23
C.I. Basic Brown 1
C.I. Disperse Yellow 7
II. Quinonoid dyestuffs
1. Quinonoid disperse and mordant dyestuffs, such as, for example,
C.I. Disperse Orange 11
C.I. Disperse Blue 5
C.I. Disperse Blue 7
C.I. Mordant Violet 26
C.I. Mordant Blue 23
III. Metal complex dyestuffs
C.I. Ingrain Blue 14
IV. Meroquinonoide dyestuffs
1. Diphenylmethane dyestuffs, such as, for example, Basic Yellow 3
2. Triphenylmethane dyestuffs, such as, for example,
C.I. Basic Violet 3
C.I. Basic Green 4
C.I. Mordant Blue 1
C.I. Mordant Blue 28
3. Quinoneimine dyestuffi, such as, for example,
C.I. Solvent Blue 22
4. Acridine dyestuffs, such as, for example, Acridine Orange 2 G
5. Thioxanthene dyestuffs, such as, for example, Pyronin G, C.I. 45005
6. Phenazine dyestuffs, such as, for example, C.I. Solvent Blue 7
7. Phenoxazine dyestuffs, such as, for example,
C.I. Mordant Blue 10
8. Phenothiazine dyestuffs, such as, for example,
C.I. Mordant Blue 51
9. Squaric acid dyestuffs, such as, for example, those known from EP-A 0 145 401
Polymethine dyestuffs comprising cationo, aniono and mero (=neutro)cyanines and hemicyanines, such as, for example,
C.I. Disperse Yellow 31
C.I. Disperse Blue 354
C.I. Disperse Red 196
C.I. Disperse Yellow 99
VI. Nitro and nitroso dyestuffs,
such as, for example,
C.I. Disperse Yellow 42
C.I. Disperse Yellow 1
VII. Heterocyclic dyestuffs
1. Perinones, such as, for example,
C.I. Disperse Yellow 58
2. Naphthalimides, such as, for example,
Disperse Yellow 11
3. Quinophthalone, such as, for example,
Disperse Yellow 54, Disperse Yellow 64
4. Coumarins, such as, for example,
those known from DE 15 94 845, 16 70 999, 20 65 076
5. Pyrazolines, such as, for example,
those known from DE 11 55 418, 14 45 705, 14 19 329
6. Stilbene dyestuffs, such as, for example,
C.I. Fluorescent Brightener 30
C.I. Fluorescent Brightener 46
In particular, the groups A can be chosen from the monovalent radicals of the following compounds:
Het1(xe2x95x90Z)n=Het2xe2x80x83xe2x80x83(I)
wherein
Het1 denotes 
Z denotes CHxe2x80x94CH or Nxe2x80x94N,
n denotes zero or 1,
Het2 denotes 
R1 denotes C1-C6-alkenyl, C5-C10-cycloalkyl or C7-C15-aralkyl,
R2 denotes C1-C6-alkyl, C1-C4-alkoxy, C6-C12-aryl, C6-C12-aryloxy, C1-C6-alkylthio, C6-C12-arylthio, mono- or di-C1-C4-alkylamino, C6-C12-arylamino, C1-C4-alkyl-C6-C12-arylamino or chlorine,
R3 denotes C1-C6-alkyl, C2-C6-alkenyl, C5-C10-cycloalkyl, C6-C12-aryl, C7-C15-aralkyl,
R4 denotes C1-C6-alkyl, C6-C12-aryl, CN, COOR3, CO-R3,
X denotes O, S, Se, NR1, CR82,
R8 denotes C1-C6-alkyl,
the asterisks characterize the position of the exocyclic Cxe2x95x90C double bond and the curved lines in the structures (5) and (6) denote hydrogen or xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94;
Het1(xe2x95x90Z)n=Het3xe2x80x83xe2x80x83(II)
wherein 
R5 denotes hydrogen, C1-C6-alkyl, C1-C6-alkoxy, fluorine or chlorine,
R6 denotes hydrogen, C1-C6-alkyl, C1-C6-alkoxy, fluorine, chlorine, CN, NO2, NHCOR3 or NHSO2R3,
Y denotes oxygen, C(CN)2, C(CN)COOR3 or 
Het1, Z, n, the asterisk and R3 have the meaning given above under (I) and
R3xe2x80x2 independently of R3 represents the meaning given above under R3; 
wherein
Y has the meaning given above under (II)xe2x80x94with the exception of oxygenxe2x80x94and additionally denotes 
X, R1, R3, R4 and the asterisk have the meaning given above under (I) and
R7 denotes hydrogen, C1-C6-alkyl, C1-C6-alkoxy, COOR3, chlorine, NO2 or CN; 
wherein
R3 and R3xe2x80x2 independently of one another have the meaning given above for R3 under (I),
R5 and R6 have the meaning given above under (II) and
Y has the meaning given above under (III),
R9 denotes hydrogen, C1-C6-alkyl, C6-C12-aryl, CN or COOR3 and furthermore additionally
R3xe2x80x2 denotes hydrogen, 
and
R3xe2x80x2 and R5 together denote xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)3xe2x80x94, xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94CH(CH3)xe2x80x94 or xe2x80x94OCH2CH2xe2x80x94; 
wherein
Het4 denotes 
W denotes xe2x80x94Nxe2x95x90Nxe2x80x94 or 
R10 denotes CN, NO2 or COOR3,
R11 denotes C1-C6-alkyl, C1-C6-alkoxy, chlorine, amino, C1-C7-acylamino or di-C1-C4-alkylamino,
R12 denotes C1-C6-alkyl, C5-C12-aryl, CN or COOR3,
R13 denotes hydrogen, CN or NO2 and R1, R2, R7, R3, R3xe2x80x2, R5 and R6 have the meaning given in the case of (I), (III) and (IV); 
xe2x80x83wherein
X1 denotes hydrogen, hydroxyl, mercapto, CF3, CCl3, CBr3, halogen, cyano, nitro, COOR19, C1-C6-alkyl, C1-C12-cycloalkyl, C1-C12-alkoxy, C1xe2x80x94C12-alkylthio, C6-C12-aryl, C6-C12-aryloxy, C6-C12-arylthio, C1-C6-alkylsulphonyl, C6-C12-arylsulphonyl, aminosulphonyl, C1-C6-alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C1-C6-alkylaminocarbonyl, phenylaminocarbonyl, NR19, R20, NHxe2x80x94COxe2x80x94R19, NHxe2x80x94SO2xe2x80x94R19, NHxe2x80x94COxe2x80x94NR19R20, NHxe2x80x94COxe2x80x94Oxe2x80x94R19 or SO2-CF3, wherein R19 and R20 independently of one another represent hydrogen, C1-C4-alkyl or phenyl,
wherein one of the radicals R1 to R13 (including R3xe2x80x2), in particular one of the radicals R1 and R3, represents a single bond which allows linkage to the group Q1, Q1 then representing a single bond in the case of the radicals R1, R3 and R3xe2x80x2.
Particularly preferred compounds (V) correspond to the formulae 
wherein Het4 represents one of the structures 26 to 33, and 
wherein Het4 represents one of the structures 26, 27, 30, 32 or 34 to 39.
As described above, the group A is bonded to the main chains of the polymers according to the invention via the intermediate members Q1, T1 and S1. The dyestuffs mentioned above can already contain these intermediate members in their entirety or in part; cf. the legend to the substituents. Dyestuff radicals which are suitable as A are therefore to be understood as the dyestuffs shortened in each case by such intermediate members already contained in the product. On the other hand, if the dyestuffs do not contain the intermediate members Q1, T1 and S1 or contain them only in part, they can be converted by appropriate reaction into the desired reactive derivatives, which are then suitable for building up the polymers according to the invention.
The unit xe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94 can thus represent, for example, xe2x80x94NR0xe2x80x94(CH2)yxe2x80x94Oxe2x80x94. For a given group A, suitable compounds of the structure Axe2x80x94NR0xe2x80x94(CH2)yxe2x80x94OH can be provided for introduction of A into polymers according to the invention or into the monomers to be polymerized. (Analogous statements apply for another meaning of Q1, T1 and S1). Such suitable compounds can thus include, for example, the following compounds: 
Additionally to the above definitions, one of the substituents R1 to R13 (including R3xe2x80x2), in particular one of the radicals R1 and R3, per radical A denotes a single bond which allows linkage to the group Q1.
The compounds
Axe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94Hxe2x80x83xe2x80x83(1)
Axe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94OCxe2x80x94CHxe2x95x90CH2xe2x80x83xe2x80x83(2)
Axe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94OCxe2x80x94C(CH3)xe2x95x90CH2xe2x80x83xe2x80x83(3)
Axe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94(CH2)nxe2x80x94OHxe2x80x83xe2x80x83(4)
Axe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94CH2xe2x80x94CHOHxe2x80x94CH3xe2x80x83xe2x80x83(5)
Axe2x80x94Q1xe2x80x94T1xe2x80x94S1xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94OHxe2x80x83xe2x80x83(6)
wherein A, Q1, T1 and S1 have the abovementioned meanings and n represents an integer from 2 to 12, and the acrylates and methacrylates of the compounds 4 to 6 are, to our knowledge, new and this invention therefore also relates to them. The compounds can be prepared by processes analogous to those for similar compounds.
The polymers according to the invention contain no groups A of the formula 
wherein
R14 to R16 independently of one another denote C1-C6-alkyl, hydroxyl, C1-C6-alkoxy, phenoxy, C1-C6-alkylthio, phenylthio, halogen, CF3, CCl3, CBr3, nitro, cyano, C1-C6-alkylsulphonyl, phenylsulphonyl, COOR1, aminosulphonyl, C1-C6-alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C1-C6-alkylaminocarbonyl or phenylaminocarbonyl,
R17 denotes halogen, C1-C6-alkyl, hydroxyl, C1-C6-alkoxy, phenoxy, C1-C4-acylamino or C1-C4-alkylsulphonylamino,
R18 denotes halogen, C1-C6-alkyl, hydroxyl, C1-C6-alkoxy or phenoxy and
X1 denotes hydrogen, hydroxyl, mercapto, CF3, CCl3, CBr3, halogen, cyano, nitro, COOR19, C1-C6-alkyl, C5-C12-cycloalkyl, C1-C12-alkoxy, C1-C12-alkylthio, C6-C12-aryl, C6-C12-aryloxy, C6-C12-arylthio, C1-C6-alkylsulphonyl, C6-C12-arylsulphonyl, aminosulphonyl, C1-C6-alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C1-C6-alkylaminocarbonyl, phenylaminocarbonyl, NR19R20, NHxe2x80x94COxe2x80x94R19, NHxe2x80x94SO2xe2x80x94R19, NHxe2x80x94COxe2x80x94NR19R20, NHxe2x80x94COxe2x80x94Oxe2x80x94R19 or SO2xe2x80x94CF3, wherein R19 and R20 independently of one another represent hydrogen, C1-C4-alkyl or phenyl.
Preferred mesogenic units M correspond to the formula 
wherein
R21 to R25 independently of one another denote hydrogen, halogen, C1-C4-alkyl, C1-C4-alkoxy, CF3, nitro, SO2CH3, SO2NH2 or cyano, wherein at least one of the substituents R21 to R25 must be other than hydrogen,
Y denotes a direct bond, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94 and
X2 denotes hydrogen, hydroxyl, mercapto, CF3, CCl3, CBr3, halogen, cyano, nitro, COOR19, C1-C6-alkyl, C5-C12-cycloalkyl, C1-C12-alkoxy, C1-C12-alkylthio, C6-C12-aryl, C6-C12-aryloxy, C6-C12-arylthio, C1-C6-alkylsulphonyl, C6-C12-arylsulphonyl, aminosulphonyl, C1-C6-alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C1-C6-alkylaminocarbonyl, phenylaminocarbonyl, NR19R20, NHxe2x80x94COxe2x80x94R19, NHxe2x80x94SO2xe2x80x94R19, NHxe2x80x94COxe2x80x94NR19R20, NHxe2x80x94COxe2x80x94Oxe2x80x94R12 or SO2xe2x80x94CF3, wherein R19 and R20 independently of one another represent hydrogen, C1-C4-alkyl or phenyl, but wherein
R21 to R25 all represent hydrogen when A corresponds to a radical of the formula (VI).
The preferred polymers according to the invention contain solely repeating units with the side groups I and II, and in particular preferably those of the formulae 
where Rxe2x95x90H or methyl.
Preferred examples of the groups T1 and T2 are, independently of one another, xe2x80x94(CH2)yxe2x80x94, xe2x80x94(CH2)mxe2x80x94CH(CH3)xe2x80x94(CH2)oxe2x80x94, xe2x80x94(CH2)mxe2x80x94C(CH3)2xe2x80x94(CH2)oxe2x80x94, xe2x80x94(CH2)mxe2x80x94Oxe2x80x94(CH2)oxe2x80x94 and xe2x80x94(CH2)mxe2x80x94N(CH3)xe2x80x94(CH2)oxe2x80x94,
wherein
y is an integer from 2 to 6 and
m and o independently of one another are integers from 0 to 2, the total of which is at least 1.
S1T1Q1 or S2T2Q2 is also preferably 
Possible preferred side groups II are, in particular, those of the formula 
wherein
X2, T2, Q2 and R21 to R25 have the abovementioned meanings.
Preferred monomers for introduction of the side groups II correspond to the formula 
wherein
n is an integer from 2 to 6,
R21 and R25 independently of one another represent H, F, Cl, Br, OH, OCH3, CH3, CF3, NO2 or CN and
at least one of the substituents R21 and R25 must be other than H, and
X2 denotes H, F, Cl, Br, CN, NO2, COOR19, C5-C12-cycloalkyl, C1-C12-alkoxy or C6-C12-aryl and
R19, R21 and R25 have the abovementioned meaning.
Examples of such monomers are 
The main chain of the side group polymers is preferably formed by monomers which carry the side groups (I), by monomers which carry the side group (II) and, if appropriate, by further monomers, the proportion of monomers which contain the side group (I) being, in particular, 25 to 80 mol %, preferably 30 to 70 mol %, the proportion of monomers which contain the side group (II) being 20 to 75 mol %, preferably 30 to 70 mol %, and the proportion of the further monomers being 0 to 50 mol %, in each case based on the total of all the monomer units incorporated.
Possible xe2x80x9cfurtherxe2x80x9d repeating units are all structural units which can be incorporated chemically into the side group polymer. They essentially serve merely to reduce the concentration of side groups I and II in the polymer and thus cause virtually a xe2x80x9cdilutionxe2x80x9d effect. In the case of poly(meth)acrylates, the xe2x80x9cfartherxe2x80x9d monomers comprise ethylenically unsaturated copolymerizable monomers, which preferably carry cc-substituted vinyl groups or xcex2-substituted allyl groups, preferably styrene; and also, for example, styrenes which are chlorinated and alkylated or alkenylated on the nucleus, it being possible for the alkyl groups to contain 1 to 4 carbon atoms, such as, for example, vinyl-toluene, divinylbenzene, xcex1-methylstyrene, tert-butylstyrenes and chlorostyrenes; vinyl esters of carboxylic acids having 2 to 6 carbon atoms, preferably vinyl acetate; vinylpyridine, vinylnaphthalene, vinylcyclohexane, acrylic acid and methacrylic acid and/or their esters (preferably vinyl, allyl and methallyl esters) having 1 to 4 carbon atoms in the alcohol component, their amides and nitriles, maleic anhydride, maleic acid half-esters and diesters having 1 to 4 carbon atoms in the alcohol component and half-amides and diamides, and cyclic imides, such as N-methylmaleimide or N-cyclohexylmaleimide; and allyl compounds, such as allylbenzene and allyl esters, such as allyl acetate, diallyl phthalate, diallyl isophthalate, diallyl fumarate, allyl carbonates, diallyl carbonates, triallyl phosphate and triallyl cyanurate.
Preferred xe2x80x9cfurtherxe2x80x9d monomers correspond to the formula 
wherein
R26 represents an optionally branched C1-C6-alkyl radical or a radical containing at least one further acrylic radical.
The polymers according to the invention can also contain more than one side group which falls under the definition of (I), or more than one side group which falls under the definition of (II), or several side groups of the definition both of (I) and of (II), and of these one side group of the definition (I) can also correspond to the formula XIII. If side chains of the structure (I) and (II) are present, at least one group Q1 or Q2 advantageously has the meaning xe2x80x94Oxe2x80x94C6H4xe2x80x94COOxe2x80x94 or xe2x80x94Oxe2x80x94C6H4xe2x80x94CONR19.
The polymers according to the invention preferably have glass transition temperatures Tg of at least 40xc2x0 C. The glass transition temperature can be determined, for example, by the method of B. Vollmer, Grundrixcex2 der Makromolekularen Chemie [Principles of Macromolecular Chemistry], pages 406-410, Springer-Verlag, Heidelberg 1962.
The polymers according to the invention in general have a molecular weight, determined as the weight average, of 5,000 to 2,000,000, preferably 8,000 to 1,500,000, determined by gel permeation chromatography (calibrated with polystyrene).
The structural elements of high shape anisotropy and high anisotropy of the molecular polarizability are the prerequisite for high values of optical anisotropy. The intermolecular interactions of the structural elements (I) and (II) are established by the structure of the polymers such that the formation of liquid crystal states of order is suppressed and optically isotropic, transparent non-scattering films can be produced. On the other hand, the intermolecular interactions are nevertheless strong enough to cause a photochemically induced, cooperative, directed reorientation process of the photochromic and non-photochromic side groups on irradiation with polarized light.
Interaction forces which are sufficient for the photoinduced change in configuration of the side group (I) to cause a reorientation of the side group (II) in the same directionxe2x80x94so-called cooperative reorientationxe2x80x94preferably occur between the side groups (I) and (II).
In the optically isotropic amorphous photochromic polymers, extremely high values of the optical anisotropy can be induced (xcex94n=0.01 to 0.2, preferably 0.01 to 0.1). The values are comparable to those which have been obtained in monodomains of liquid crystal polymers, or are even greater than these. They are significantly greater in comparison with amorphous polymers without these structural elements.
States of order are generated and modified in the side group polymers, and their optical properties are thus modulated, by the influence of actinic light.
Linearly polarized light, the wavelength of which is in the range of the absorption band of the side groups (I) whose configuration can be varied by photoinduction is preferably used as the light.
The preparation of the side group monomers and their polymerization can be carried out by processes known from the literature (for example DD 276 297, DE 3 808 430, Makromolekulare Chemie [Macromolecular Chemistry] 187, 1327-1334 (1984), SU 887 574, Europ. Polym. 18 561 (1982) and Liq. Cryst. 2, 195 (1987)).
Isotropic films can be produced without the need for expensive orientation processes utilizing external fields and/or surface effects. They can be applied to substrates by spin coating, dipping, casting or other coating processes which are easy to control technologically, can be introduced between two transparent sheets by pressing or flowing in, or can simply be prepared as a self-supporting film by casting or extrusion. Such films can also be produced from liquid crystal polymers which contain the structural elements in the context described by sudden cooling, that is to say by a cooling rate of  greater than 100 K/minute, or by rapid stripping of the solvent.
The layer thickness is preferably between 0.1 xcexcm and 1 mm, in particular between 0.5 and 100 xcexcm.
The photoinduced orientation of the side groups or the writing of information is effected by irradiation with actinic light suitable for the group A whose configuration can be varied by photoinduction. This leads to an angle-dependent photoselection, which causes reorientation of the photochromic groups andxe2x80x94by a cooperative effectxe2x80x94a continuous reorientation of the permanently shape-anisotropic side groups M in the same direction up to the maximum of perpendicular with respect to the electrical vector of the stimulating light.
The exposure to light can take place over the whole surface or locally with linearly polarized, coherent or non-coherent, monochromatic light, the wavelength of which is in the absorption range of the side groups A whose configuration can be varied by photoinduction.
The information can be written in point form with a laser or in unstructured form over the whole surface with a laser or a lamp or using a mask or by writing in a holographic refractive index grid at an intensity of 1 to 500 mW/cm2 over a period of between 1 and 30,000 seconds.
The reorientation process is exceptionally effective. The change in birefringence xcex94n which can be achieved below Tg is preferably 0.01 to 0.20, in particular 0.05 to 0.10.
The high values of the photochemically induced birefringence and of the photochemically induced dichroism result from the molecular structure of the side groups and the cooperative mechanism of the photoinduced orientation to a state of the same macroscopic orientation of the photochromic and non-photochromic but permanently shape-anisotropic side groups.
The preferred orientation can be chosen as desired, and depends solely on the choice of the direction of the electrical vector of the stimulating light with reference to the polymer substance. The extent of the orientation at a constant temperature and wavelength depends solely on the irradiated energy, which can be varied either via the time or, within certain limits, via the output of the light source. The orientation, the birefringence and the dichroism are thus parameters which can be chosen as desired and can be reproduced exactly under constant framework conditions during repeated writing and deletion.
A reproducible, defined, continuously variable birefringence of long-term stability can be produced in the side chain polymers. It can be shown as a defined contrast in transmission in the polarized light. If polymers with side groups with dichroic properties are used, a dichroism of the absorption or of the emission can correspondingly be produced reproducibly and in a defined and continuously variable manner. A uniform orientation is produced in the entire polymer film by uniform irradiation conditions. If the irradiation conditions, such as energy dose and polarization direction, vary locally, a film which is structured in respect of the preferred orientation of the side groups is produced, which leads to pixels of different optical anisotropy.
The preferred direction in the orientation distribution of the optically anisotropic film can be reversed again by exposure to non-polarized actinic light, and the optical isotropy along the perpendicular to the surface can be reestablished. Renewed irradiation with the same source but a changed position of the electrical vector with reference to the polymer film leads to a modification of the direction and magnitude of optical anisotropy. The system can in this way be switched repeatedly between two different states with respect to the direction and magnitude of the optical anisotropy.
On the basis of these effects, a medium for reversible, optical data storage is in principle available with the polymers described. As with the production of the films, all measures for reestablishing the monodomain are dispensed with even after deletion of the information.
The polymers can be used for digital or analog data storage in the broadest sense, for example for optical signal processing, for Fourier transformation and folding or in coherent optical correlation techniques. The lateral resolution is limited by the wavelength of the reading light. It allows a pixel size of 1 to 100 xcexcm.
This property makes the polymers particularly suitable for processing images and for information processing by means of holograms, reproduction of which can be effected by illuminating with a reference beam. The interference pattern of two monochromatic coherent light sources with a constant phase relationship can be stored analogously and a higher storage density can be produced in the storage medium owing to the relationship between the electrical vector of the light and the associated preferred direction. Three-dimensional holographic images can correspondingly be stored. Read-out is achieved by illuminating the hologram with monochromatic, coherent light. In the case of analog storage, grey scale values can be established continuously and with local resolution. Read-out of information stored in analog form is effected in polarized light, it being possible to bring out the positive or negative image, depending on the position of the polarizers. In this case, on the one hand the contrast of the film produced by the phase shift of the ordinary and extraordinary beam can be utilized between two polarizers, the planes of the polarizer advantageously forming an angle of 45xc2x0 to the plane of polarization of the writing-in light and the plane of polarization of the analyser being either perpendicular or parallel to that of the polarizer. Another possibility is detection of the deflection angle of the reading light caused by induced birefringence.
The polymers can be used as optical components which can be passively or optically switchable. Thus, the high photoinduced optical anisotropy can be utilized for modulation of the intensity and/or of the state of polarization of light. Components which have imaging properties comparable to lenses or gratings can correspondingly be produced from a polymer film by holographic structuring. The polymers can furthermore be employed for the production of polarizers.
The invention thus also relates to the use of the polymers described for optical components. Polarizers are also to be regarded as such optical components.
The polymers according to the invention can be prepared in the customary manner by free radical copolymerization of the monomers in suitable solvents, such as, for example, aromatic hydrocarbons, such as toluene or xylene, aromatic halogenated hydrocarbons, such as chlorobenzene, ethers, such as tetrahydrofuran and dioxane, ketones, such as acetone and cyclohexanone, and/or dimethylformamide, in the presence of polymerization initiators which supply free radicals, such as, for example, azodiisobutyronitrile or benzoyl peroxide, at elevated temperatures, as a rule at 30 to 130xc2x0 C., preferably 40 to 70xc2x0 C., as far as possible with exclusion of water and air. They can be isolated by precipitation with suitable agents, for example methanol. The products can be purified by reprecipitation, for example with chloroform/methanol.
The polymers according to the invention can form self-supporting films.
Preferably, however, they are applied to carrier materials, for example glass or films of plastic. This can be effected by various techniques known per se, the process being chosen according to whether a thick or thin layer is desired. Thin layers can be produced, for example, by spin coating or knife coating from solutions or the melt, and thicker layers can be produced by filling prefabricated cells, melt pressing or extrusion.